1. Field of the Invention
The present invention relates to a display device, and particularly, to a display device including a thin film transistor in each pixel.
2. Description of the Related Art
For example, in a liquid crystal display device of an active matrix type, substrates are disposed so as to be opposed via liquid crystal, and gate lines extending in an x direction are disposed in parallel in a y direction and data lines extending in the y direction are disposed in parallel in the x direction on a surface of one of the substrates on a liquid crystal side. Further, a region surrounded by the gate lines and the data lines serves as a pixel region, and the pixel region includes at least the thin film transistor to be turned on by a signal (scanning signal) from the gate line and a pixel electrode to which a video signal from the data line is supplied via the turned-on thin film transistor.
In this case, the thin film transistor, the gate line, the data line, the pixel electrode, and the like are formed by stacking a conductive layer, a semiconductor layer, an insulating film, and the like processed into desired patterns using selective etching by a photolithography technology on a substrate in a desired order.
The display device thus configured is required to reduce the number of laminated films and to reduce the number of processes for selective etching by the photolithography technology in order to achieve flexibility and reduce costs.
In response to those demands, for example, there is known a technology in which an oxide semiconductor layer is used as a semiconductor layer which forms a channel of a thin film transistor, and the data line and the pixel electrode which are each formed of a conductive film are directly connected to the oxide semiconductor layer.
Such a display device described above is disclosed in, for example, JP 2004-349583 A.
However, in the display device described in JP 2004-349583 A, the data line and the pixel electrode are formed of the same conductive film. Thus, for example, in a case where the data line and the pixel electrode are formed of a transparent conductive film such as Indium Tin Oxide (ITO), the display device inevitably has high electric resistance in the data line.
Further, in a case where an opaque conductive film made of metal or the like is used as the conductive film, there is a disadvantage in that the opaque conductive film cannot be applied to a transmissive liquid crystal display device using a backlight.